Multiple inert gas elimination technique

By using more than two gases with different solubilities in blood a better resolution of VA/Q can be obtained, allowing a multicompartmental analysis. This can be achieved with the multiple inert gas elimination technique (Hedenstierna 1.995). Ventilation and blood flow can be allocated to a number (e.g. 50) of hypothetical compartments ranging from shunt (VA/Q= 0) through compartments with low, normal, and high VA/Q ratios to dead-space (VA/Q= ¥). The procedure is based on the measurement of the retention and elimination of several (usually six) 'inert' gases (gases obeying Henry's law, i.e. showing a linear relationship between partial pressure and concentration in blood) with different solubilities in blood. The resulting VA/Q distribution will depend on both gravitational and non-gravitational distributions of ventilation of blood flow but does not allow any spatial analysis. Rather, the VA/Q distribution can be considered as a fingerprint of the lung's ability to transfer gas between alveoli and capillary blood. Examples of VA/Q distributions in a healthy subject, both awake and during anesthesia, are shown in the lower panels of Fig 3